The FBI has processed more than 100 leads in its investigation into the weekend massacre at a gay bar in Orlando, Florida, with agents probing the electronic records of the man responsible for the worst mass shooting in U.S. history.

The shooting, which left 49 victims and the gunman dead, has prompted a full anti-terrorism response from the U.S. government, with investigators from several agencies seeking to understand the motive behind the attack and any possible links to terrorism groups.

“No stone will be left unturned as we'll follow the leads wherever they take us,'' Paul Wysopal, special agent in charge for the FBI's Tampa division, told reporters Monday in Orlando. Wysopal, who said the FBI would be conducting a shooting reconstruction at the Pulse nightclub where the attack took place, said it was too early to tell if intelligence officials missed any red flags about the shooter, who had previously been interviewed by law enforcement agents.

“We've been collecting a great amount of electronic and physical evidence,'' said U.S. Attorney Lee Bentley. “If anyone else was involved in this crime, they will be prosecuted.''

State and local law enforcement planned to spend Monday identifying the victims and contacting family members of the deceased. So far, family members of about half of the 49 victims have been contacted, officials said.

President Barack Obama, who on Sunday called the shooting “an attack on all of us,'' planned to receive a briefing from FBI Director James Comey and other top security officials at the White House on Monday. Florida Governor Rick Scott asked Obama to declare a state of emergency for Florida.

The gunman armed with an assault-type weapon and a handgun opened fire at Pulse at around 2 a.m. on Sunday. The suspect, who was shot dead by police, has been identified by law enforcement authorities and relatives as Omar Mateen, a 29-year-old U.S. citizen of Afghan descent from Fort Pierce, Florida.

Mateen called 911 during the shooting and pledged his allegiance to the Islamic State, said Orlando Police Chief John Mina. He also told police that he had explosives inside the club, Mina said.

The massacre hit a nerve on several of the hot-button topics facing the U.S., including approaches to gun control, global terrorism and immigration. Republican presidential nominee Donald Trump and his probable Democratic opponent, Hillary Clinton, on Monday traded barbs in a round of television interviews.

Trump told Fox News that the nightclub massacre, the worst in the U.S. since the Sept. 11, 2001 attacks, means “it's absolute war but we don’t have uniforms.'' He said Obama should resign because he wouldn't even use the term “radical Islam'' in his address and he attacked Obama and Clinton on their policies because “tens of thousands of people are pouring into our country and many of them are no different” from suspected shooter.

Trump said he's getting congratulations for “being right on radical Islamic terrorism," having advocated a temporary ban on allowing Muslims to enter the U.S. Trump said the U.S. also needs to step up surveillance of mosques.

Clinton, meanwhile, took Trump to task for politicizing the tragedy.

“This is a moment for Republicans, Democrats and all Americans to work together as one team,'' she said in an interview with CNN Monday. She said “statesmanship, not partisanship'' is needed now, reflecting on how Americans came together after the Sept. 11 attacks. “We should capture that spirit.''

Clinton used the occasion to push what she called “common-sense gun control reform.'' As part of that, Congress should reinstate the assault weapons ban, which was allowed to lapse.

She dismissed Trump's focus on using the term “radical Islam.'' “From my perspective, it matters what we do more than what we say,'' she said. “It matters that we got Bin Laden, not what we called him.''

What Clinton won't do is “to demonize and demagogue and declare war on an entire religion.''

Trump plans a "major speech" in New Hampshire on Monday to address the Orlando attack, immigration and national security, his campaign said in an e-mailed statement. Clinton will speak about the shooting, and the steps she would take to keep Americans safe, at an event in Cleveland on Monday and at subsequent campaign stops.

Both Clinton and Obama called the shooting a hate crime, having come at a gay nightclub on a weekend when many cities are holding pride parades and celebrations. Separately, an Indiana man was arrested with a cache of weapons, ammunition and explosive-making materials at the Los Angeles gay pride parade.

“We will keep fighting for your right to live freely, openly and without fear,” Clinton said. “Hate has absolutely no place in America.”

Obama said the attack is “especially heartbreaking” for citizens who are lesbian, gay, bisexual or transgender. “It was more than a nightclub, it was a place of solidarity,” he said of the shooting venue.

It is also a reminder of how easy it is to obtain weapons under U.S. law, the president said.

“The shooter was apparently armed with a handgun and a powerful assault rifle,” the president said. “This massacre is therefore a further reminder of how easy it is for someone to get their hands on a weapon that lets them shoot people in a school, or in a house of worship, or a movie theater, or in a nightclub."

“We have to decide if that’s the kind of country we want to be,” Obama added. “And to actively do nothing is a decision as well.”

Senator Bob Casey, a Pennsylvania Democrat, said he will introduce a new bill Monday to extend an existing ban on convicted felons from buying guns to include anyone convicted of a misdemeanor hate crime.

Clinton and Obama canceled a joint campaign event scheduled for Wednesday in Green Bay, Wisconsin, because of the shooting, according to an e-mailed release.

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Representative Adam Schiff of California, the top Democrat on the House Intelligence Committee, said in a statement that Islamic State leadership has been urging attacks during the Muslim Ramadan period, and that local law enforcement officials had told him that the shooter had made known his allegiance to the group. “Whether this attack was also ISIS-directed, remains to be determined,” Schiff said.

The gunman called 911 moments before the shooting and spoke about the Islamic State, Ronald Hopper, an FBI assistant special agent in charge of the bureau’s Orlando office, said at a news conference Sunday.

The FBI had twice investigated Mateen for possible links to Islamic terrorists, closing both inquiries because it found no hard connections, Hopper said.

Until Sunday, the worst mass shooting in the U.S. was the 2007 rampage on the Virginia Tech campus in Blacksburg, Virginia, that left 32 people dead and 30 injured.

—With assistance from Rakteem Katakey in London and Tamara Thueringer in Washington.